This invention relates to an improvement in a transducer assembly for transmitting pulses of pressure waves into a body of a patient and/or receiving reflections of portions of the acoustical energy contained in those pulses and producing corresponding electrical pulses that can be used to form an image. A transducer assembly designed for these purposes may be comprised of a linear array of transducer elements, usually piezoelectric crystals, mounted in spaced parallel relationship along a line on an acoustic energy absorbing base with their lengths perpendicular to the line, or it may be comprised of annular piezoelectric crystals mounted in concentric spaced relationship on a base. Ideally, the linear array would transmit a beam of acoustic energy within a plane that is perpendicular to the crystals and the base so as to strike targets within the plane but not above or below it, and the annular array would transmit a beam of acoustic energy only along its axis. While neither ideal can be fully realized, it has been found helpful to focus the acoustic beam. Various means for this purpose have been tried. The faces of the crystals remote from the base have been shaped but this is difficult to do. Single element lenses have been formed with epoxy, styrene or silicone rubber but each has one or more of the following disadvantages: improper acoustic impedance match with the body of the patient, susceptibility to chemical attack, or insufficient strength or hardness to protect the fragile crystals of the array. Unfortunately, materials that provide the best protection do not have the desired acoustic impedance.